The present invention generally relates to the detection and profiling of subterranean geophysical structures and/or properties. More specifically, the present invention relates to a system and method for detecting and profiling subterranean geophysical structures and/or properties using sequences of coded pulses in a monocycle waveform.
Profiling of subterranean geophysical structures and/or properties is essential to the seismic survey industry. Seismic surveys are a primary exploration tool used to determine whether subsurface geologic conditions are favorable for finding accumulations of oil and gas. Conventional technologies used in seismic surveys generally rely on the introduction of acoustic shock waves deep into the subsurface of the earth and the detection of reflected waves at the surface.
Shock waves are introduced into the ground through the use of either explosives or a vibration coupler. The explosive method sends a broadband pulse into the ground and the resulting spatial echoes are collected by a large systematic grid field of seismic sensors, alternatively, known as geophones. Due to the inherent, dangerous nature of explosives, this method necessarily requires careful planning and a significant amount of setup time.
Apart from the time-consuming preparation, the explosive method has at least a number of operational shortcomings. First, in order to impart greater clarity in shadow zones, many different detonations must be performed. Further, the explosive process has the undesirable effect of producing nonlinear results. The detonation of explosives necessarily compresses the earth, thereby masking details which would otherwise be made visible. Therefore, it would be desirable to provide a system and method that requires less preparation and produces better results.
The second method of introducing shock waves into the ground uses a vibration coupler. The vibration coupler generally comprises a large hydraulic motor with an offset weight used to impart a vibration into the ground. Such vibration coupler generally has a time-varying structure that is usually proprietary to the company that manufactures the vibration coupler. Furthermore, a 5- or 10-ton truck is usually required to move the vibration coupler from site to site. Therefore, it would be desirable to provide a system and method that is convenient to transport from location to location.
The present invention relates to a system and method for detecting and profiling geophysical structures and/or properties. The system includes an impulsive seismic source, an echo detector for sensing data that are representative of the echoes returned by the geophysical structures and/or properties. The impulsive seismic source generates a sequence of coded pulses in a monocycle waveform. The sequence of coded pulses propagates to the geophysical structures and/or properties, causing them to return a number of echoes. These echoes are captured and processed to produce an image which is representative of the profiled geophysical structures and/or properties.
The present invention can be used in a variety of industries, especially, in the burgeoning market for the acquisition, processing and analysis of 3-dimensional and 4-dimensional seismic survey data in connection with locating, mapping and managing reservoirs of subsurface hydrocarbons. The present invention can also be employed to locate salt domes and other subsurface geologic strata that may contain petroleum or natural gas, kimberlite pipes (diamonds), magnetite and certain phosphates. It can further be employed to detect and locate underground aquifers, subterranean tunnels, caverns, fractures and faults. Furthermore, the present invention can also be applied to the detection of near-surface buried objects, such as underground storage tanks, utility pipes and mains, and for the neutralization of buried ordnace such as antipersonnel land mines.
Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to accompanying drawings.